It’s a 2D shooter, so it’s not at all reliant on being able to understand text. A button for shoot, a button for alternate attack, and a button for bomb. Avoid bullets. Any Japanese text that does show up isn’t important to being able to fully enjoy the game.

Milestone only releases in Japan though, they’d have to have another publisher pick up the game for localization (like UFO for the US Milestone Shooting Collection, or O3 for the US Gamecube Chaos Field).

And we don’t know if 3DS games are region locked, but there are strong suspicions that it is (unlike DS or GBA).